Re: [PATCH 2/3] dt-bindings: rtc: add chargeable flag for rx8130

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Hi,

On 24/08/2020 15:32:22+0200, Bastian Krause wrote:
> On 8/24/20 1:31 PM, Bastian Krause wrote:
> > 
> > On 4/15/20 8:56 PM, Alexandre Belloni wrote:
> >> On 15/04/2020 18:37:00+0200, Bastian Krause wrote:
> >>> Signed-off-by: Bastian Krause <bst@xxxxxxxxxxxxxx>
> >>> ---
> >>>  Documentation/devicetree/bindings/rtc/rtc-ds1307.txt | 3 +++
> >>>  1 file changed, 3 insertions(+)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/rtc/rtc-ds1307.txt b/Documentation/devicetree/bindings/rtc/rtc-ds1307.txt
> >>> index 66f0a31ae9ce..987a0c9e0cd7 100644
> >>> --- a/Documentation/devicetree/bindings/rtc/rtc-ds1307.txt
> >>> +++ b/Documentation/devicetree/bindings/rtc/rtc-ds1307.txt
> >>> @@ -34,6 +34,9 @@ Optional properties:
> >>>  - trickle-diode-disable : ds1339, ds1340 and ds 1388 only
> >>>  	Do not use internal trickle charger diode
> >>>  	Should be given if internal trickle charger diode should be disabled
> >>> +- aux-voltage-chargeable: rx8130 only
> >>> +	Epsons's rx8130 supports a backup battery/supercap.
> >>> +	This flag tells	whether the battery/supercap is chargeable or not.
> >>>  
> >>
> >> I think we should make that a generic property and this should supersede
> >> trickle-diode-disable which is a bit wonky as I would prefer the default
> >> to be disabled instead of enabled with the current semantics.
> > 
> > Alright, I think I know how to transform the RTC drivers.
> > 
> > One question about the DTs though:
> > 
> > This means we should remove "trickle-diode-disable" from all upstream
> > DTs and add "aux-voltage-chargeable" to all upstream DTs that use a RTC
> > compatible whose driver care in their probe function for
> > "trickle-diode-disable", right?
> 
> Sorry, forget that.
> 
> Here's the situation:
> 
> Currently there is a switch to explicitly disable charging, so the
> default is to charge. We cannot introduce another boolean switch to turn
> that the other way around, because that would change the default and
> break backwards compatibility.
> 
> The only way I can think of is to introduce "aux-voltage-chargeable" not
> as a boolean switch but as an integer, without any default. If this
> property is not available, the drivers should simply do what they did
> prior to this change (look for the legacy trickle-diode-disable, use the
> default they used before).
> 
> Are you okay with that?
> 

I agree boolean should be avoided in RTC drivers because we need a way
to express "don't change this value".

> Some more context:
> 
> I originally tried to add a chargeable flag for rx8130. Prior to this
> patch, there was no need to set "trickle-diode-disable" for this,
> because the driver did not pass the chargeable flag to the RTC. With the
> patch the default would have been to charge as long as
> "trickle-diode-disable" is not there. So there's a change in behavior.
> 

Yes, IIRC, my point was simply to move the documentation for
aux-voltage-chargeable to the generice rtc binding documentation,
Documentation/devicetree/bindings/rtc/rtc.yaml

For now, you sould keep support for trickle-diode-disable but it has to be
superseded by aux-voltage-chargeable if present. Is that more clear?


-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com



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